In recent years, control systems have been adopted which are aimed at saving wires in an FA (factory automation) system and which interconnect various types of control equipment via a network. In industrial machinery, in particular, drivers for driving various axis motors making up the drive section of the machinery and input/output devices included in peripheral equipment are interconnected via a network as control target apparatuses and controlled by a motion controller.
FIG. 15 is a schematic view showing a general structure of such a network type motion control. In FIG. 15, a master controller (called the master hereunder) 201 for overall control and slave controllers (called the slaves hereunder) 202 for directly driving control target apparatuses are interconnected via a network 203. The master 201 has a program execution unit executing control programs, and a master communication unit communicating with the slaves 202 via the network 203 in order to input signal status 204 of sensors or the like in the slaves 203 as well as to output commands 205 for operating the control target apparatuses such as motors.
Here, the program execution unit of the master executes control programs stored in, say, a memory at predetermined intervals (called the control cycle hereunder). A growing number of control target apparatuses (i.e., number of slaves) and increasingly complicated control processes contribute to prolonging the control cycle of the master. While communications between the master and the salves are conducted also at predetermined intervals (called the communication cycle hereunder), the growing slave count tends to prolong the communication cycle of the network as well.
Generally, the control cycle of the master is set to an integral multiple of the communication cycle. The control cycle of the master determines the responsiveness of the control system, i.e., a delay time (latency) that elapses from the time a status change is detected in the input signal from sensors or the like until the time machinery operation is actually changed accordingly.
Thus, improving the responsiveness of the control system in the past required shorting the communication cycle of the network and the control cycle of the master, i.e., improving the communication speed over the network and boosting the arithmetic capacity of the master. However, this method has posed the problem of raising the cost of the control system.
For this conventional network type motion controller, there exists a known method described in Patent Literature 1 cited below. With this method, a servo response management unit separate from a servo command issuance processing unit determines whether or not a termination condition suitably established irrespective of the execution of axis movement commands within a motion program is met. If the termination condition is determined to be met, the servo response management unit notifies the servo command issuance processing unit thereof and executes a different command in order to enhance the speed of a servo command issuing process.